1. Field of the Invention
The present invention relates to a single plate type color image pickup device.
2. Description Related to the Prior Art
A single plate type color image pickup device is known in which red, green, and blue color filters are disposed on a plurality of pixels according to a predetermined pattern (refer to U.S. Pat. No. 8,134,633 corresponding to Japanese Patent Laid-Open Publication No. 2009-088255). In the single plate type color image pickup device, a signal of an arbitrary color pixel is subjected to an arithmetic process. The signal of the pixel is complemented with color information of the remaining two colors of pixels in the vicinity of thereof. Therefore, it is possible to obtain a full color image in which each pixel has three colors of signals.
In the color image pickup device according to the U.S. Pat. No. 8,134,633, square pixels are arranged in a lattice. The color filters are provided on the pixels in a Bayer pattern.
In the Bayer pattern, as shown at the top left of FIG. 19, out of four pixels arranged in a square lattice of 2×2, green color filters 200G are assigned to the two diagonal pixels, and a red color filter 200R and a blue color filter 200B are assigned to the remaining two pixels on a one-by-one basis, to compose a basic unit 202 of an array pattern. By sequentially arranging the basic units 202 in accordance with the position of the pixels, an imaging surface is formed in the square lattice for suitable use in the color image pickup device. Note that, in drawings of this application, “R” represents the red color filter. “G” represents the green color filter. “B” represents the blue color filter.
In the color image pickup device according to the U.S. Pat. No. 8,134,633, each pixel is provided with a microlens. Furthermore, the diameter of the microlens provided on the red color filter is increased with increase in a distance from a middle of the imaging surface to a periphery. This is for the sake of preventing a color shading phenomenon caused by a infrared cut filter used together with the color image pickup device. The infrared cut filter, which uses a multilayer interference thin film, shifts a transmission wavelength band to a short wavelength side in regard to oblique incident light having a large incident angle. Thus, a cut wavelength band of the oblique incident light extends to a red region of the visible light range, and hence a red signal is decreased. This phenomenon tends to occur in the periphery of the imaging surface having the large incident angle. As a result, an image becomes bluish relatively in the periphery of the imaging surface. This causes deterioration in image quality of the color image pickup device.
Accordingly, as described in the U.S. Pat. No. 8,134,633, the diameter of the microlenses of the pixels having the red color filters is increased in the periphery of the imaging surface, in order to increase an incident light amount and enhance a relative pixel sensitivity. Precluding decrease in the red signal due to the infrared cut filter offers a good balance among the signals of each color, and prevents the occurrence of the color shading phenomenon caused by the infrared cut filter. The color image pickup device of the U.S. Pat. No. 8,134,633 improves the image quality in this manner.
As shown in FIG. 19, in the Bayer pattern, there is no blue color filter 200B in a line 204 in which the green color filters 200G and the red color filters 200R are vertically aligned in an alternate manner, and in a line 205 in which the green color filters 200G and the red color filters 200R are horizontally aligned in an alternate manner. Likewise, there is no red color filter 200R in a line 206 in which the green color filters 200G and the blue color filters 200B are vertically aligned in an alternate manner, and in a line 207 in which the green color filters 200G and the blue color filters 200B are horizontally aligned in an alternate manner.
There is no red color filter 200R and no blue color filter 200B in a line 208 in which only the green color filters 200G are diagonally aligned. There is no green color filter 200G in a line 209 in which the red color filters 200R and the blue color filters 200B are diagonally aligned in an alternate manner.
In the Bayer pattern, as described above, each of the lines 204 to 209 of the pixels has a nonexistent color. For this reason, the Bayer pattern has a problem that pseudo color that is a wrong color not existing in actual fact tends to be produced in a part having a high spatial frequency of an object and a boundary part of colors. This problem is caused by an array pattern of the color filters provided on the pixels, and therefore cannot be solved by making an adjustment to the diameter of the microlenses and the like.
To prevent the occurrence of the pseudo color, each of the vertical, horizontal, and diagonal lines of the pixels has to include the color filters of every color. However, unless the array pattern of the color filters has regularity, the arithmetic process of the color information becomes complicated and requires much time to produce an image. Therefore, in the color image pickup device, another array pattern of the color filters is desired that can prevent the occurrence of the pseudo color, as compared with the Bayer pattern, without complicating the arithmetic process.